Everything Science Grade 12

7.2 CHAPTER 7. MECHANICAL PROPERTIES OF MATTER

Example 3: Hooke’s Law III

QUESTION

A spring has a spring constant of− 400 N.m−^1. By how much will it stretch if

a load of 50 N is applied to it?

SOLUTION

F =−kx

50 =−(−400)x

x =

50

400

= 0,125 m

= 12,5 cm

Deviation from Hooke’sLaw ESCDN

We know that if you have a small spring and youpull it apart too much itstops ’work-
ing’. It bends out of shape and loses its springiness. When this happens, Hooke’s Law
no longer applies, the spring’s behaviour deviates from Hooke’s Law.

Depending on what type of material we aredealing with, the manner in which it
deviates from Hooke’sLaw is different. We give classify materials bythis deviation.
The following graphs show the relationship between force and extensionfor different
materials and they all deviate from Hooke’s Law. Remember that a straight line show
proportionality so as soon as the graph is no longer a straight line, Hooke’s Law no
longer applies.